1. Field of the Invention
The present invention relates to a display device for controlling display gradation in each display dot of a liquid-crystal display device or the like on the basis of image data (gradation data) written in an image memory such as a VRAM, and a display device comprising the display control device.
2. Description of the Related Art
FIG. 9 is a block diagram showing an arrangement of a conventional display device.
Referring to FIG. 9, a screen size of a liquid-crystal display panel (to be referred to an "LCD panel" hereinafter) 1 is represented by 320 (horizontal).times.240 (vertical) pixels. Each pixel is constituted by three dots, i.e., a red (R) dot, a green (G) dot, and a blue (B) dot.
An image data storage unit 3a constituted by an IC memory such as a VRAM or the like has a storage capacity of 320.times.240.times.3.times.4=921,600 bits=115,200 bytes. With respect to each display dot (320.times.240.times.3 dots) of the LCD panel 1, 4-bit gradation data is allocated. With this arrangement, on each display dot of the LCD panel 1, a gradation display having 16 gradation levels, i.e., (0000)2 to (1111)2, can be performed. Referring to FIG. 9, as the image data storage unit 3a, two image data storage units for front and rear screens are arranged to perform a screen switching process.
When a driver 102 receives gradation data (DA) from a controller 105 in synchronism with a clock, corresponding display dots are sequentially driven such that a gradation display represented by the gradation data can be obtained.
In the above arrangement, a CPU 4 writes arbitrary image data (gradation data of one screen) in the image data storage unit 3a.
On the other hand, each time the controller 105 receives a predetermined frame signal (pulse signal having an interval of 1/150 sec), the controller 105 sequentially reads gradation data in the image data storage unit 3a from a start address, and transfers the read gradation data to the driver 102 together with the address of the gradation data.
The driver 102 is driven such that display dots corresponding to the transferred address perform a gradation display represented by the transferred gradation data.
Each time the frame signal is input, the above process is repeated, an image corresponding to image data written by the CPU 4 is displayed on the LCD panel 1.
In the above conventional display device, each time the controller 105 receives a frame signal, the controller 105 loads all gradation data in the image data storage unit 3a, and transfers all the loaded gradation data to the driver 102. For this reason, when the screen size of the LCD panel 1 is large (for example, as shown in FIG. 9, 320 (horizontal).times.240 (vertical) pixels or the like), an amount of data to be transferred between the image data storage unit 3a and the controller 105 and between the controller 105 and the driver 102 is considerably large.
As a result, in the conventional display device, a current consumed in the data transfer considerably increases.